Smoking articles in which an aerosol is generated by the transfer of heat from a combustible heat source to a physically separate aerosol-generating material are known in the art. The aerosol-generating material may be located within, around or downstream of the heat source. In use, the combustible heat source of the smoking article is lit and volatile compounds are released from the aerosol-generating material by heat transfer from the combustible heat source. The released volatile compounds are entrained in air and drawn through the smoking article upon puffing. The formed aerosol is inhaled by the consumer.
It is desirable for a combustible heat source suitable for use in a smoking article to have certain attributes to enable or enhance the smoking experience.
For example, the heat source should produce enough heat during combustion to allow release of a flavoured aerosol from an aerosol-generating material, but still be sufficiently small to fit within a smoking article that may be of a similar size as a conventional lit-end cigarette.
Furthermore, the heat source should be capable of burning with a limited amount of air until the fuel in the heat source is expended and should also produce as little as possible or substantially no carbon monoxide, nitrogen oxides or other potentially undesirable gases upon combustion.
In addition, the ignition temperature of the heat source should be sufficiently low that the heat source is readily ignitable under normal lighting conditions for a conventional lit-end cigarette using, for example, a match or conventional cigarette lighter.
The heat source should also have an appropriate thermal conductivity. If too much heat is conducted away from the burning zone of the heat source to other parts of the heat source during combustion, combustion at the burning zone of the heat source will cease when the temperature drops below the extinguishment temperature of the heat source. Therefore, a heat source with too high a thermal conductivity may undesirably be difficult to ignite and, after ignition, subject to premature self-extinguishment. The thermal conductivity of the heat source should be at a level that, in use, allows effective heat transfer to the aerosol-generating material without conducting too much heat to any means or structure by which it is fixed, mounted or otherwise incorporated in the smoking article.
The heat source should also not disintegrate before or during use and should be able to withstand small mechanical stresses that may occur as a result, for example, of a consumer dropping the smoking article.
It would be desirable to provide a composite heat source suitable for use in smoking articles that meets some or all of the above requirements.
It would further be desirable to provide a composite heat source capable of catalysing the decomposition of one or more potentially undesirable gases produced during combustion thereof.
It would also be desirable to provide a composite heat source capable of retaining particulate matter produced during combustion thereof.